The oxidative stress caused by nitric oxide (NO) in the brain has been proposed as a pathogenic mechanism in Alzheimer's disease. Endothelial NO synthase (ecNOS) produces the majority of circulating NO. The biological functional and genetic association studies suggested that the Glu298Asp polymorphism of the ecNOS gene (NOS3) may be a genetic risk factor for late-onset Alzheimer's disease (LOAD). To investigate an association between the NOS31 Glu298Asp polymorphism and sporadic LOAD in Chinese, we examined 338 LOAD patients and 378 healthy controls. The associations of the Glu/Glu genotype and Glu allele with LOAD (chi2 = 9.12, df = 1, P = 0.003 by genotype; chi2 = 8.37, df = 1, P = 0.038 by allele) were found. After stratifying by apolipoprotein E allele 4 (APOE epsilon 4) status, increased LOAD risks associated with the Glu/Glu genotype and Glu allele only in the APOE epsilon 4 noncarriers (chi2 = 6.28, df = 1, P = 0.012 by genotype; chi2 = 5.62, df = 1, P = 0.018 by allele) were seen. These results suggest that the NOS3 gene Glu298Asp polymorphism might be a risk factor for LOAD and dependent on APOE epsilon 4 status in Chinese.